This application is based upon and claims benefit of priority of Japanese Patent Application No. 2001-58721 filed on Mar. 2, 2001, the content of which is incorporated herein by reference.
1. Field of the Invention
The present invention relates to a commutator for an electric rotary machine, and more particularly to a commutator in which commutator segments positioned symmetrically with respect to a rotor shaft center are electrically connected to each other through a connecting member.
2. Description of Related Art
A commutator of this type is disclosed in JP-A-11-187622 and JP-A-11-187623. Even number of commutator segments (more than four) are cylindrically disposed around a rotor shaft, and commutator segments positioned symmetrically with respect to the rotor shaft, forming pairs of commutator segments, are electrically connected through connecting members. Each connecting member includes a pair of terminals, each connected to each segment, and a ring-shaped conductor portion connecting the pair of terminals. The pair of terminals and the ring-shaped conductor portion are integrally formed.
In such a commutator, it is necessary to provide a number of connecting members corresponding to a number of segment pairs because each pair of commutator segments is connected through a separate connecting member. For example, if a commutator has six commutator segments, three connecting members are necessary. Therefore, a larger number of connecting members are required as the number of segments become larger, and accordingly the commutator size becomes large and its manufacturing cost becomes high.
In a commutator in which segments are cylindrically disposed on an outer periphery of the commutator, it is possible to provide a large number of connecting members because an axial length of the commutator is long enough to accommodate the large number of connecting members. However, in a commutator in which segments are positioned on an end surface perpendicular to the rotor shaft, it is difficult to accommodate a large number of connecting members in a commutator because its axial length is short.
The present invention has been made in view of the above-mentioned problem, and an object of the present invention is to provide an improved commutator in which each pair of segments positioned symmetrically with respect to a rotor shaft are electrically connected to each other in a simple manner without enlarging the commutator size.
A commutator having even number (2n) of commutator segments is mounted on a rotor of an electric rotary machine such as a direct current motor. The commutator segments are electrically insulated from one another. The 2n commutator segments form n pairs of commutator segments, each pair consisting of two segments positioned symmetrically with respect to the rotor axis. The commutator segments in each pair are electrically connected to each other. The commutator segments are disposed on a rotor end surface which is perpendicular to the rotor axis. Alternatively, the commutator segments may be cylindrically disposed around the rotor axis.
The commutator is manufactured by integrally molding a metallic base plate and a segment plate made of carbon with a resin material and by forming slits for separating individual commutator segments. The commutator segments are electrically insulated from one another, while the commutator segments belonging to each pair are electrically connected through respective connecting portions formed integrally with the metallic base plate. N connecting portions are formed on the metallic base plate before the metallic base plate is molded together with the segment plate. The connecting portions are depressed from a surface of the metallic base plate by a distance larger than a thickness of the metallic base plate, so that they are not separated in the process of making the separating slits.
Since the n connecting portions are formed on the metallic base plate, the electrical connection of two commutator segments in each pair is easily made without providing separate n pieces of connecting members. Further, the 2n commutator segments are separated from a single segment plate by the separating slits. Therefore, the commutator is made compact and is manufactured in a simple and inexpensive process.
Other objects and features of the present invention will become more readily apparent from a better understanding of the preferred embodiment described below with reference to the following drawings.